Ultrasonic image processing apparatus

ABSTRACT

There is provided an ultrasound image processing apparatus which displays an ultrasonic image with a higher resolution. In a received frame, a first pixel array, a second pixel array, and a third pixel array are defined in depths different from each other. For each pixel of interest on the first pixel array, a pattern matching process is applied between the first pixel array and the second pixel array, to calculate a mapping address on the second pixel array for the pixel of interest. In addition, for each pixel of interest on the third pixel array, a pattern matching process is applied between the third pixel array and the second pixel array, to calculate a mapping address on the second pixel array for each pixel of interest. The second pixel array is re-constructed into a high-density pixel array using pixel values and mapping addresses of a plurality of pixels of interest.

BACKGROUND

Technical Field

The present invention relates to an ultrasonic image processingapparatus, and in particular to a technique for improving resolution orquality of ultrasonic images.

Background Art

An ultrasonic image processing apparatus is formed, for example, as anultrasound diagnosis apparatus or an information-processing device. Inthe information-processing device, image data provided from theultrasound diagnosis apparatus are processed. In the following, anultrasound diagnosis apparatus will be described. An ultrasounddiagnosis apparatus is an apparatus which transmits and receivesultrasound to and from a living body, and which forms an ultrasonicimage based on received information acquired by the transmission andreception of the ultrasound. As an ultrasonic image, a two-dimensionaltomographic image, a two-dimensional bloodstream image, athree-dimensional image, or the like are known.

More specifically, an imaginary scan plane is formed by electronicscanning of the ultrasonic beam in a living body. With this process, areceived frame (received frame data) corresponding to the beam scanplane is acquired. The received frame comprises a plurality of beam datasets arranged in a beam scan direction, and each beam data set comprisesa plurality of echo data sets arranged in a depth direction. In otherwords, the received frame comprises a two-dimensionally placed group ofecho data (echo data array). An individual echo data point is an elementof the received frame, and is generally called a “pixel”. An element ofa display frame to be described later is also generally called a pixel.

Each of the pixels of the received frame has an address conforming witha transmission/reception coordinate system (a polar coordinate system inthe case of electronic sector scanning). In order to convert thereceived frame into a display frame; that is, in order to convert fromthe transmission/reception coordinate system to a display coordinatesystem (orthogonal coordinate system), the ultrasound diagnosisapparatus is equipped with a scan converter (JP 2003-299651 A). Inaddition to the coordinate conversion function, the scan converter hasan interpolation processing function, a frame rate adjusting function,or the like.

In order to improve the quality of the ultrasonic image, it is desirableto increase the resolution or density of the received frame. However, ifthe number of beam data sets of one received frame (echo data density)is increased, the received frame rate would be reduced. An inter-frameinterpolation process or an inter-line interpolation process may beapplied to the received frame, to increase the pixel density or the linedensity. However, in the related art, a simple linear interpolationprocess has been used as such interpolation processes, and, therefore,even though an amount of data appears to be increased, the quality ofthe ultrasonic image cannot be sufficiently improved.

In beam scanning methods such as sector scanning, convex scanning,radial scanning, etc., a beam array of a fan shape or a radial shape isformed, and the beam spacing is widened for deeper sites. In the scanconverter described above, a large number of pixels required for thedisplay frame are generated by interpolation calculation. Therefore, alarge number of interpolation pixels are embedded in a deep portion inthe display frame. Thus, in such a deep portion, although pixelinsufficiency does not occur, there has been a problem in that the imageis blurred. More specifically, there has been a problem in that theimage shifts or deforms in the beam scan direction. A similar problemoccurs when a three-dimensional image is formed.

SUMMARY

An advantage of the present invention is that a density of an ultrasonicimage is increased, to improve image quality.

Another advantage of the present invention is that, when a scanningmethod in which an ultrasonic beam array is formed in a fan shape or aradial shape is executed, image quality is improved in the ultrasonicimage, in particular, in a deep portion of the image.

According to one aspect of the present invention, there is provided anultrasonic image processing apparatus comprising an in-frame processorwhich applies a process between a first pixel array and a second pixelarray in a frame acquired by transmitting and receiving ultrasound, andwhich calculates a movement destination on the second pixel array foreach pixel of interest in the first pixel array, and a re-constructingunit which re-constructs the second pixel array into a high-densitypixel array using the movement destination calculated for each pixel ofinterest.

With the above-described configuration, the density of the second pixelarray can be increased using information in the first pixel array. Inother words, because of continuity of the tissue on the beam scan plane,a local pixel value pattern observed on a certain pixel array and alocal pixel value pattern observed on another pixel array nearby tend tobe similar to each other. Therefore, the data of the former pixel arraycan be used to improve the latter pixel array. In particular, the methodis preferably applied between two pixel arrays that are adjacent inspace. By incorporating the content of a first pixel array into asecond, adjacent pixel array, the resolution of the content of thesecond pixel array can be improved. With this process, for example, anoutline and a boundary can be emphasized. More specifically, first, thein-frame process is used to calculate a movement destination (orcorresponding position) on the second pixel array, for a plurality ofpixels forming an entirety of or a part of the first pixel array. Withthis process, an additional group of pixels which are imaginarily oractually mapped can be defined or considered on the second pixel array.With the additional group of pixels, the pixel density of the secondpixel array can be increased. The high-density pixel array may bere-constructed by simply adding the additional group of pixels to theoriginal group of pixels of the second pixel array, or the high-densitypixel array may be re-constructed by newly calculating a group ofinterpolation pixels using the original group of pixels and theadditional group of pixels, and based on the original group of pixelsand the group of interpolation pixels. In the former case, the originalgroup of pixels (that is, the second pixel array) and the additionalgroup of pixels may be handled without distinction, or, alternatively,the original group of pixels and the additional group of pixels may bemanaged separately in view of the convenience of the data process. Forexample, in the scan conversion of the frame, in addition to theoriginal group of pixels, pixel values and movement destinations ofpixels forming the entirety of or a part of the frame may also beconsidered.

With the above-described configuration, there can be created a situationas if the real pixel is increased on the pixel array can be created inplace of simple increase of apparent number of pixels by the linearinterpolation process, or a situation where the number or density of thereal pixels referred to in the interpolation process is increased priorto the interpolation process. Therefore, a high-quality image with ahigh resolution can be formed, and problems such as blurring of theimage can be effectively resolved or reduced.

The above-described ultrasonic image processing apparatus is, forexample, an ultrasound diagnosis apparatus which executes ultrasounddiagnosis in real time on a living body, or an information-processingdevice which processes data acquired in such an ultrasound diagnosisapparatus. The pixel on each frame is a frame element, and represents anecho intensity, Doppler information, etc. The density increasing processis preferably applied prior to the conversion from atransmission/reception coordinate system to a display coordinate system.

According to another aspect of the present invention, preferably, eachof the first pixel array and the second pixel array includes a pluralityof pixels arranged in a beam scan direction, a depth of the first pixelarray and a depth of the second pixel array differ from each other, andthe high-density pixel array includes a larger number of pixels than anumber of formations of received beams in the beam scan direction.Preferably, the first pixel array and the second pixel array areadjacent to each other in the depth direction. The received beam isformed by a phase alignment and summation process, and, normally, one ora plurality of received beams are formed for one transmitting beam.

According to another aspect of the present invention, preferably, thein-frame processor calculates the movement destination of the pixel ofinterest by applying a pattern matching process between the first pixelarray and the second pixel array. A thickness of the first pixel arrayand the second pixel array in the depth direction is preferably onepixel, but the thickness may alternatively correspond to a plurality ofpixels. In such a case also, the one-dimensional pattern matchingprocess is preferably applied as the pattern matching process.Alternatively, a two-dimensional pattern matching process may beemployed.

According to another aspect of the present invention, preferably, thein-frame processor comprises a correlation value profile generating unitwhich generates a correlation value profile as a result of the patternmatching process for each pixel of interest in the first pixel array,and a correspondent address calculating unit which calculates acorrespondent address on the second pixel array as the movementdestination based on the correlation value profile for each pixel ofinterest in the first pixel array. With the use of the correlation valueprofile, it becomes possible to estimate the true best value based onthe shape or the like of the profile, and a position corresponding tothe true best value can be determined as the correspondent address.According to another aspect of the present invention, preferably, thecorrespondent address is a correspondent address with a fractionalvalue, including an integer part corresponding to an integer multiple ofan original pixel spacing in the second pixel array and a fractionalvalue smaller than the original pixel spacing. In order to calculate thefractional value, for example, a sub-pixel process is employed.

According to another aspect of the present invention, preferably, there-constructing unit re-constructs the high-density pixel array by aninterpolation process based on an original group of pixels of the secondpixel array and an additional group of pixels defined by a pixel valueand the correspondent address with fractional value for each pixel ofinterest. The original group of pixels includes real pixels, and theadditional group of pixels includes real pixels which exist on anotherline. The latter pixels are individually mapped on optimum positions ona line of interest so that the resolution or the pixel density can beimproved.

According to another aspect of the present invention, preferably, ahigh-density frame is formed by re-constructing a plurality of pixelarrays of the frame into a plurality of high-density pixel arrays, andthe high-density frame includes a plurality of sets of original beamdata and a plurality of sets of interpolation beam data. With thisconfiguration, the pitch in the pixel array can be unified and the loadin the subsequent calculation can be reduced. The interpolation processon the second pixel array and the scan conversion can be applied at thesame time. In other words, based on the group of pixels of the secondpixel array and the pixel values and the correspondent addresses of theplurality of pixels of the first pixel array, the display frame can beconstructed with one calculation. In this case, however, the calculationduring the scan conversion becomes complex, and, therefore, it ispreferable to apply the scan conversion process after generating thehigh-density frame.

According to another aspect of the present invention, preferably, thepixel of interest is selected in a partial region in the first pixelarray, and the high-density pixel array is a pixel array in a part ofwhich the density is increased. With this configuration, the densityincreasing process can be applied on a portion where the resolution islow or a portion for which observation at a high resolution is desired,to thereby shorten the calculation time or reduce the calculation load.

According to another aspect of the present invention, preferably, thein-frame processor calculates, by a process between the second pixelarray and a third pixel array in the frame acquired by transmitting andreceiving ultrasound, a movement destination on the second pixel arrayfor each pixel of interest in the third pixel array, and there-constructing unit re-constructs the second pixel array into thehigh-density pixel array using the movement destination calculated foreach pixel of interest in the first pixel array and the movementdestination calculated for each pixel of interest in the third pixelarray. With this configuration, the real pixel can be imaginarily oractually mapped from previous and subsequent pixel arrays (first pixelarray and third pixel array) to an intermediate pixel array (secondpixel array), to thereby improve the intermediate pixel array.

According to another aspect of the present invention, preferably, theframe is a frame which conforms with a transmission/reception coordinatesystem, a high-density frame is formed by repeatedly applying there-construction of the high-density pixel array, and there is provided aconversion unit which generates a display frame which conforms with adisplay coordinate system from the high-density frame. According toanother aspect of the present invention, preferably, the frame comprisesan ultrasonic beam array which is spread radially, and the high-densityframe includes a plurality of interpolation lines which are added atleast in a deep portion of the frame.

According to another aspect of the present invention, preferably, theframe is a frame which is acquired in real time or a frame which is readfrom a cine memory. The cine memory is normally a large-capacity memorywhich stores a large number of frames in time sequential order, andpreferably has a ring-buffer structure. By applying the densityincreasing process on real time data, the image quality of theultrasonic image which is displayed in real time can be improved. Byapplying the density increasing process on the data which are read fromthe cine memory, the image quality of replayed image can be improved.

According to another aspect of the present invention, preferably, theultrasonic image processing apparatus further comprises a unit whichapplies a pre-process to increase density of the frame by an inter-frameinterpolation process before the frame is input to the in-frameprocessor According to another aspect of the present invention,preferably, the ultrasonic image processing apparatus further comprisesa unit which applies a post-process to further increase the density of ahigh-density frame generated by repeatedly applying the re-constructionof the high-density pixel array or to further increase the density of adisplay frame acquired based on the high-density frame.

According to another aspect of the present invention, there is providedan ultrasonic image processing apparatus comprising an in-frameprocessor which applies a process between a first pixel array and asecond pixel array in a frame which is acquired by transmitting andreceiving ultrasound and which conforms with a transmission/receptioncoordinate system, and which calculates a movement destination on thesecond pixel array for each pixel of interest in the first pixel array,and a conversion unit which applies a process to convert the frame whichconforms with the transmission/reception coordinate system into adisplay frame which conforms with a display coordinate system, and whichrefers to a pixel value for each pixel of interest and the movementdestination for each pixel of interest during the conversion process.

According to another aspect of the present invention, there is providedan ultrasonic image processing program comprising a module which appliesa process between a first pixel array and a second pixel array in aframe acquired by transmitting and receiving ultrasound, and whichcalculates a movement destination on the second pixel array for eachpixel of interest in the first pixel array, and a module whichre-constructs the second pixel array into a high-density pixel arrayusing the movement destination calculated for each pixel of interest.The modules correspond to function units forming the program. Theabove-described program is stored in a recording medium such as amemory, a CD-ROM, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a basic structure of an ultrasonicimage processing apparatus (ultrasound diagnosis apparatus) having adensity increasing function.

FIG. 2 is a conceptual diagram for explaining an operation of a densityincreasing unit of an inter-frame processing type shown in FIG. 1.

FIG. 3 is a conceptual diagram illustrating a movement of a tissuebetween frames.

FIG. 4 is a flowchart showing a sequence of steps of a pattern matchingprocess between frames.

FIG. 5 is a conceptual diagram illustrating a pattern matching processbetween frames.

FIG. 6 is a diagram showing an example of a correlation value profile.

FIG. 7 is a diagram showing a first example of a sub-pixel process.

FIG. 8 is a diagram showing a second example of a sub-pixel process.

FIG. 9 is a conceptual diagram showing a two-dimensional mapping address(movement destination).

FIG. 10 is a conceptual diagram illustrating an imaginary mappingprocess result between frames.

FIG. 11 is a conceptual diagram illustrating an interpolation pixeladdress generated by a line interpolation process.

FIG. 12 is a conceptual diagram illustrating a frame with the increaseddensity after the interpolation process.

FIG. 13 is a conceptual diagram illustrating a beam interpolationprocess for a beam data array which spreads radially.

FIG. 14 is a conceptual diagram illustrating a partial beaminterpolation process.

FIG. 15 is a block diagram showing a first example structure of thedensity increasing unit shown in FIG. 1.

FIG. 16 is a block diagram showing a second example structure of thedensity increasing unit shown in FIG. 1.

FIG. 17 is a block diagram showing a third example structure of thedensity increasing unit shown in FIG. 1.

FIG. 18 is a block diagram showing a first alternative configuration ofthe basic structure shown in FIG. 1.

FIG. 19 is a block diagram showing a second alternative configuration ofthe basic structure shown in FIG. 1.

FIG. 20 is a block diagram showing a basic structure of an ultrasonicimage processing apparatus (ultrasound diagnosis apparatus) havinganother density increasing function.

FIG. 21 is a diagram showing a beam data array.

FIG. 22 is a conceptual diagram for explaining an operation of a densityincreasing unit of an in-frame processing type in relation to theultrasonic image process apparatus shown in FIG. 20.

FIG. 23 is a flowchart showing a sequence of steps of a pattern matchingprocess in a frame.

FIG. 24 is a conceptual diagram illustrating a pattern matching processin a frame.

FIG. 25 is a conceptual diagram illustrating a one-dimensional mappingaddress (movement destination).

FIG. 26 is a conceptual diagram illustrating an imaginary mappingprocess result between lines.

FIG. 27 is a conceptual diagram illustrating a pixel array (line) havingincreased density after the interpolation process.

FIG. 28 is a block diagram showing an example configuration of thedensity increasing unit shown in FIG. 20.

FIG. 29 is a conceptual diagram for explaining boundary emphasisachieved by the density increase.

FIG. 30 is a block diagram showing an example combination of two typesof density increasing processes.

FIG. 31 is a block diagram showing another example configuration of twotypes of density increasing processes.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the drawings.

(1) Density Increasing Using Inter-Frame Pattern Matching Process

FIG. 1 is a block diagram showing an ultrasound diagnosis apparatusserving as an ultrasonic image processing apparatus. The ultrasounddiagnosis apparatus is used in the medical field, and is an apparatuswhich forms an ultrasonic image based on a received signal which isacquired by transmitting and receiving ultrasound to and from a livingbody. As the ultrasonic image, a two-dimensional tomographic image, atwo-dimensional bloodstream image, a three-dimensional image, etc. areknown.

In an example configuration of FIG. 1, a probe 10 comprises aone-dimensional (1D) array transducer. The 1D array transducer comprisesa plurality of transducer elements arranged in a straight line shape oran arc shape. An ultrasound beam B is formed by the 1D array transducer,and the ultrasound beam B is electrically scanned. In the presentembodiment, the probe 10 is a convex type probe, and the ultrasound beamis convex-scanned. Alternatively, a sector scanning method may beemployed, or other electronic scanning methods such as radial scanningand linear scanning may be employed. The “density increasing process” tobe described later is preferable in particular when a plurality ofultrasound beams are formed radially. The probe 10 is used while incontact on a body surface in the example configuration of FIG. 1.Alternatively, the probe 10 may be a body cavity insertion type probe.

A transmitting unit 12 is a transmitting beam former. That is, thetransmitting unit 12 supplies a plurality of transmitting signals to theprobe 10 in parallel to each other during transmission. With thisprocess, a transmitting beam is formed by the 1D array transducer; thatis, the ultrasound is radiated into the living body. During reception, areflected wave from the inside of the living body is received by the 1Darray transducer. A plurality of received signals are output from the 1Darray transducer to a receiving unit 14 in parallel to each other. Thereceiving unit 14 is a received beam former, and applies a phasealignment and summation process on the plurality of received signals, togenerate beam data corresponding to the received beam. The receivedsignal serving as the beam data are output to a signal processor 16. Thesignal processor 16 comprises modules such as a wave detection unit, alogarithmic conversion unit, etc. The wave detection unit is a modulewhich converts an RF received signal into a received signal in abaseband range.

As will be described later, a density increasing unit 18 of aninter-frame processing type is a unit which applies a pattern matchingprocess between frames that are adjacent to each other in time, toincrease the density or resolution of each frame. In the presentembodiment, the density increasing process is applied to a frame (framedata) after the wave detection. Alternatively, the density increasingprocess may be applied to the RF signal. One frame (frame data)comprises a plurality of beam data sets, and each beam data setcomprises a plurality of data sets (frame elements). In the presentspecification, an individual frame element is referred to as a “pixel”.Each pixel is data representing an echo brightness. Alternatively, eachpixel may represent Doppler information. A high-density frame which isformed by the density increasing unit 18 is output to a digital scanconverter (DSC) 20.

The DSC 20 has a coordinate conversion function, a pixel interpolationfunction, a frame rate adjusting function, etc. With the DSC 20, thereceived frame conforming with the transmission/reception coordinatesystem is converted into a display frame conforming with a displaycoordinate system. In the present embodiment, the display frame isformed based on the high-density received frame. Therefore, the qualityof the ultrasonic image displayed on a screen can be significantlyimproved. A display processor 22 has a function to combine graphic dataor the like on image data formed by the DSC 20, and the display dataformed by the display processor 22 are output to a display unit 24. Acontroller 26 comprises a CPU and an operation program, and controlsoperations of the elements shown in FIG. 1. An inputting unit 28 isformed with an operation panel in the example configuration shown inFIG. 1. The function of the density increasing unit 18 shown in FIG. 1may alternatively be realized with software. Although not shown in FIG.1, a cine memory is provided between the signal processor 16 and thedensity increasing unit 18. The cine memory is a memory whichtemporarily stores a plurality of frames in time sequential order, andhas a ring buffer structure. The density increasing unit 18 applies aprocess on a frame acquired in real time, and similarly processes aframe which is read from the cine memory. Alternatively, the cine memorymay be provided between the density increasing unit 18 and the DSC 20 ordownstream of the DSC 20. In an ultrasonic image processing apparatuswhich processes data which are output from an ultrasound diagnosisapparatus, a program corresponding to the density increasing unit 18shown in FIG. 1 is executed.

FIG. 2 shows a conceptual diagram for an operation of the densityincreasing unit 18 shown in FIG. 1. In FIG. 2, a frame array 30 shown atthe upper part is a frame array before the density increasing process,and comprises a plurality of frames arranged in time sequential order.In the example configuration of FIG. 2, each frame is a two-dimensionaldata array acquired at a given scan plane position in the living body.Alternatively, the frame array may be acquired while moving the scanplane. The density increasing unit applies a pattern matching process(refer to reference numeral 36) between frames. Specifically, between aprevious frame 34 and a current frame 32, a pattern matching process isapplied for each pixel of interest on the previous frame 34 (a pixelthat becomes a copy source). With this process, a two-dimensionalmovement vector is determined for each data point on the previous frame34 (refer to reference numeral 38). The two-dimensional movement vectorshows a movement destination of the pixel of interest; that is, acorrespondent address or a mapping address on the current frame 32.

For each pixel on the previous frame 34, an imaginary mapping or anactual mapping to the current frame 32 is executed, and the currentframe 32 is re-constructed based on the result of the mapping, so thatthe current frame 32 becomes a high-density frame. More specifically, aswill be described later, a line interpolation process is applied basedon the group of pixels of the current frame 32 and the group of pixelsafter mapping, so that the high-density frame is formed (refer toreference numeral 40). A group of high-density frames 42 is shown at alower part of FIG. 2. The group of high-density frames 42 includes aplurality of high-density frames 44. Each high-density frame 44 isformed with a plurality of beam lines which are originally present and aplurality of interpolation lines which are added. That is, theresolution or the density is increased. The DSC described above appliesconversion to the display frame on each high-density frame 44 (refer toreference numeral 46). In the example configuration shown in FIG. 1, thedensity increasing process is applied before the coordinate conversion.

In the linear interpolation process of the related art, an interpolationline is generated simply between two beam lines, and, when such aprocess is applied, there has been a problem such as the image beingblurred or the image being shifted in the electrical scan direction.With the above-described process, the real pixel on the previous frameis used in an augmented manner as a part of the pixels of the currentframe, so that the current frame can be made a high-quality frame. Inparticular, when a plurality of beam lines are set radially, the beamspacing is increased in a deep region, and there has been a problem ofreduction of the image quality at the deep region, but with theabove-described process, a large number of real pixels can be directlyor indirectly embedded between lines, and, therefore, the image qualitycorresponding to a deep portion in the body can be significantlyimproved. Here, the real pixel means an original pixel (beforecoordinate conversion) acquired by the transmission and reception of theultrasound, as opposed to an imaginary pixel which is generated incalculation during the coordinate conversion.

The density increasing process will now be described in more detail withreference to FIG. 3 and subsequent drawings.

FIG. 3 shows a movement of a tissue between frames. In (A1), a beam dataarray conceptualized in the real space is shown. The beam data arraycomprises a plurality of sets of beam data 48, with each set of beamdata 48 having a plurality of data points (that is, pixels). Parameter rrepresents a depth direction and parameter θ represents a beam scandirection. Reference numeral 52 represents a specific tissue present inthe body. In (A2), a beam data array conceptualized in a signalprocessing space is shown. A plurality of sets of beam data 48 arearranged in the θ direction. White circles 50 and black circles 58respectively represent pixels, and, in particular, the black circles 58represent pixels within the tissue. In other words, a group of the blackcircles 58 shown by reference numeral 56 in the signal processing spacecorrespond to the tissue 52 in the real space.

In (B1), a beam data array which is acquired one time phase later isshown. Reference numeral 54 represents the tissue in this time phase,and reference numeral 52A represents the tissue in the previous timephase (refer also to reference numeral 52 in (A)). In (B2), blackcircles represent pixels within the tissue, and a group of the blackcircles is specified with reference numeral 60. As is clear fromcomparison of the group 56 and the group 60, the movement of the tissuebetween the frames is very small, and, thus, mapping of the past pixelon the current frame is allowed. With such a mapping process, theresolution of the current frame can be significantly improved.Alternatively, a pixel of interest may be set in the current frame, andthe pixel of interest may be mapped onto the past frame.

FIG. 4 is a flowchart showing a pattern matching process applied in thedensity increasing unit shown in FIG. 1. First, in S10, a pixel ofinterest is set on a previous frame, and, in S12, a template is set onthe previous frame. Specifically, FIG. 5 shows in (A) a previous frame,individual pixels in the previous frame are set as a pixel of interest62 in order, and a template 64 is set for each pixel of interest 62 as apredetermined region centered at the pixel of interest 62. In S14 ofFIG. 4, a search area is set on the current frame, and in S16, areference area is set in the search area. Specifically, FIG. 5 shows in(B) the current frame, where reference numeral 62A represents acorrespondent point corresponding to the pixel of interest 62. A searcharea 66 is set with a predetermined size and centered at thecorrespondent point 62. A reference area 68 is set in the search area66. The reference area 68 has the same shape and the same size as thetemplate 64. While a position of the reference area 68 is sequentiallyshifted, a pattern matching process to be described below is applied ateach position.

Specifically, in S18 of FIG. 4, the pattern matching process is appliedbetween the template which is set on the previous frame and thereference area which is set on the current frame. The pattern matchingprocess is more specifically a correlation process. For example, acorrelation value is calculated using the following equation (1) orequation (2). Here, equation (1) calculates a sum of squared differences(SSD) as the correlation value and equation (2) calculates a sum ofabsolute differences (SAD) as the correlation value.

$\begin{matrix}{R_{SSD} = {\sum\limits_{j = 0}^{N - 1}{\sum\limits_{i = 0}^{M - 1}( {{I( {i,j} )} - {T( {i,j} )}} )^{2}}}} & (1) \\{R_{SAD} = {\sum\limits_{j = 0}^{N - 1}{\sum\limits_{i = 0}^{M - 1}{{{I( {i,j} )} - {T( {i,j} )}}}}}} & (2)\end{matrix}$

In the equations described above, M and N represent sizes of thetemplates. That is, M and N represent numbers of pixels in thetemplates. T(i, j) represents a pixel value of each pixel in thetemplate. I(i, j) represents a pixel value of a pixel in the referencearea.

The above-described pattern matching process is repeatedly applied whilesetting the reference area on each area position in the search area,and, when it is judged in S20 of FIG. 4 that the reference area has beenset for all area positions, S22 is executed. In S22, a mapping addresswith a fractional value (movement destination) is calculated for thepixel of interest based on a two-dimensional correlation value profilerepresenting the correlation values acquired for the area positions bythe pattern matching process. In the present embodiment, a sub-pixelprocess to be described later is applied in S22, and, with this process,a fractional value (fractional value address) which is smaller than theunit address; that is, the unit pixel, is identified.

This process will now be described with reference to FIG. 6. FIG. 6shows the two-dimensional correlation value profile. A number in eachcell represents the correlation value. Among a plurality of correlationvalues, the numerical value shown by Q1 (80) is the smallest value, andis an apparent smallest correlation value (that is, apparent bestcorrelation value). However, as can be deduced from the correlationvalue profile of FIG. 6, the actual smallest correlation value Q2 is notnecessarily at the position shown by Q1, and, in many cases, is deviatedfrom this position. In consideration of this, in the present embodiment,in order to improve the mapping precision, and, consequently, the imagequality, the sub-pixel process is applied to the two-dimensionalcorrelation value profile. Specifically, a combination of an integeraddress and a fractional value address is specified as the mappingaddress. Here, a basic unit of the integer address corresponds to thepixel or a pitch between pixels. The fractional value address is a fineraddress of less than the unit pixel. The sub-pixel process will bedescribed later with reference to FIGS. 7 and 8.

In FIG. 4, in S24, it is judged whether or not the above-describedprocess has been applied for all pixels of the current frame, and, whenit is judged that the process is not completed for all pixels, theprocesses from S10 are repeatedly applied. In other words, the nextpixel is set as the pixel of interest (the pixel of interest isupdated), and the matching process or the like described above isapplied for the new pixel of interest. In the example process of FIG. 4,all pixels of the current frame are set as the pixel of interest.Alternatively, only the pixels of a partial region in the previous framemay be set as the pixel of interest. For example, only the pixelsexisting in a deep region may be set as the pixel of interest, and aline interpolation process may be applied only to such a deep region.

FIG. 7 shows a first example of the sub-pixel process, and FIG. 8 showsa second example of the sub-pixel process. FIGS. 7 and 8 showone-dimensional sub-pixel processes, but in reality, a two-dimensionalsub-pixel process is applied.

The sub-pixel process shown in FIG. 7 is based on an isogonal linefitting method. Reference numeral 136 shows a smallest value (bestvalue), reference numeral 142 shows a second smallest value, andreference numeral 138 represents a third smallest value. A horizontalaxis represents displacement, with a unit of one pixel. A vertical axisrepresents the correlation value. In the isogonal line fitting method,first, a straight line 140 passing through the smallest value 136 andthe third smaller value 138 is defined. Next, a straight line 144 whichis an inverted straight line in which the slope of the straight line 140is inverted and which passes through the second smallest value 142 isdefined. Then, an intersection 146 of the two straight lines 140 and 144is identified. A sub-pixel estimate value 148 is determined as aposition where the intersection 146 exists. The sub-pixel estimate value148 has, in addition to the normal integer address, a fractional valueaddress.

In a parabola fitting method shown in FIG. 8, first, a second-orderfunction (parabola curve) passing through the smallest value 136, thesecond smallest value 142, and the third smallest value 138 is defined.Then, in the second-order function, a position 151 of an axis ofsymmetry is identified. The position 151 is set as a sub-pixel estimatevalue 152. These sub-pixel estimation methods are exemplary, and thesub-pixel estimate values may alternatively be determined through othermethods.

Next, a line interpolation process which is applied following thepattern matching process will be described with reference to FIGS. 9-12.

FIG. 9 shows a correspondence relationship of pixels. The previous frameis shown in (A), and the current frame is shown in (B). By thecalculation of the mapping address with fractional value for each pixeldescribed above, a mapping position (copy destination position) isdetermined for each pixel of the previous frame. In FIG. 9, blackcircles represent pixels within the tissue, and white circles representother pixels. These pixels are both pixels on the beam line. A trianglerepresents a position of the pixel (correspondent position) after themapping. More specifically, a pixel 70 on the previous frame correspondsto a position 72 on the current frame, and this relationship is shown byreference numeral 74. Similarly, a pixel 76 in the previous framecorresponds to a position 78 in the current frame, and thecorrespondence relationship is shown by reference numeral 80. A pixel 82in the previous frame corresponds to a position 84 in the current frame,and the correspondence relationship is shown by reference numeral 86.The pixel on the previous frame may be actually mapped onto the currentframe, or, alternatively, the correspondence relationship may be managedand referred to as data. In either case, by increasing the number ofpixels of the current frame, the precision of the line interpolationcalculation can be improved.

FIG. 10 shows a result of imaginary mapping. Reference numeral 90represents a real pixel on a beam line 88, and reference numeral 92represents a pixel added by mapping. These pixels are used for the lineinterpolation process. More specifically, FIG. 11 shows a plurality ofinterpolation lines 94 which are additionally set for the plurality ofsets of beamdata (beam lines). Each interpolation line has a pluralityof interpolation points or interpolation pixels 96. By applying the lineinterpolation process based on the plurality of real pixels 90 and theplurality of additional pixels (real pixels on the previous frame) 92, aframe after line interpolation (high-density frame) as shown in FIG. 12can be acquired. The real pixels 90 exist on the beam line 88. Aplurality of interpolation pixels 98 exist on each interpolation line94. If all of the real pixels and the interpolation pixels are alignedin this manner; that is, if the high-density frame has an orderlytwo-dimensional arrangement, the next scan conversion process can beapplied quickly and easily. Alternatively, the scan conversion processmay be applied using the plurality of real pixels after mapping shown inFIG. 10. Alternatively, it is also possible to not actually executecopying of the pixels of the previous frame, to refer to the pluralityof pixel values and the plurality of mapping addresses of the pixels ofthe previous frame, and to apply the scan conversion process on thecurrent frame.

FIG. 13 shows an effect of the line interpolation process describedabove. In (A), a state before the line interpolation process is shown,and, in (B), a state after the line interpolation process is shown.Reference numeral 100 represents a display matrix, and each intersection105 existing in the display matrix represents a position of a displaypixel. As shown in (A), a beam data array 106 before the interpolationprocess includes a plurality of sets of beam data 107, each of which hasa plurality of real pixels 108. As the depth becomes deeper, the linespacing is widened. If a simple linear interpolation process is appliedand a plurality of interpolation pixels are embedded, the problem ofsignificant degradation of the image quality tends to occur. On theother hand, as shown in (B), a beam data array 110 forming thehigh-density frame includes a plurality of interpolation lines 106 inaddition to the plurality of original beam data (beam lines) 107. Morespecifically, an interpolation line is inserted between adjacent beamlines. Because of this, the density of the pixels referred to in thescan conversion process can be increased, in particular, in a deepportion in the living body, and the image quality after the scanconversion process can be improved particularly in the deep portion. Inother words, the problem of shifting of the image in the beam scandirection or blurring of the image by the scan conversion process can beprevented or reduced.

FIG. 14 shows a result of application of the line interpolation processon a portion (a deep portion) in a depth direction. In other words, theline interpolation process is applied to a partial range 114 in thedepth direction. Reference numeral 111 represents a beam line, andreference numeral 112 represents an interpolation line. Theinterpolation line is generated only in the partial range 114, and, withthis configuration, data are effectively added only in the region whereinterpolation is necessary. From a different point of view, data may bereduced for portions where the interpolation process is not asnecessary. With this process, an effective scan conversion process canbe executed.

FIG. 15 shows a first example structure of the density increasing unitshown in FIG. 1. The previous frame (previous frame data) is stored in aprevious frame memory 118. The current frame (current frame data) isstored in a current frame memory 120. Alternatively, the matchingprocess may be applied not between adjacent frames, but between framesdistanced from each other by one or a plurality of frames.

A matching processor 122 applies the pattern matching process betweenframes as described above. With this process, the two-dimensionalcorrelation value profile for each pixel of the previous frame isacquired, and is stored in a correlation value profile memory 124. Thesub-pixel process is applied by a sub-pixel processor 126 on thetwo-dimensional correlation value profile for each pixel of interest.With this process, an address on the current frame (mapping address withfractional value) corresponding to the pixel of the previous frame isdetermined for each pixel of the previous frame. This data are stored ina memory 128.

A mapping processor 130 identifies, for each pixel of the previousframe, an address to which the pixel is to be mapped, by referring tothe address with fractional value stored in the memory 128, and writesthe pixel value of the pixel on the corresponding address on a memory132. That is, the pixels of the previous frame are mapped with a newarrangement in a two-dimensional memory space of the mapping data memory132. An interpolation processor 134 applies the line interpolationprocess described above based on the current frame stored in the currentframe memory 120 and the mapping data stored in the mapping data memory132. With this process, the high-density frame is generated. In otherwords, the current frame is re-constructed into the high-density frame.

In a second example structure of the density increasing unit shown inFIG. 16, the mapping of pixels of the previous frame is not actuallyexecuted, the pixel value and the address with fractional value arereferred to for each pixel of the previous frame, and the lineinterpolation process is applied on the current frame by aninterpolation processor 154 based on the pixel value and the addresswith fractional value. The same reference numerals are assigned tocommon elements shown in FIG. 15, and description of these elements willnot be repeated. This applies similarly to the below-described drawings.

In a third example structure of the density increasing unit shown inFIG. 17, a first frame memory 156, a second frame memory 158, and athird frame memory 160 are connected in series. The first frame memory156 stores the previous frame, the second frame memory 158 stores anintermediate frame, and the third frame memory 160 stores a subsequentframe. A matching processor 162 applies the matching process between theprevious frame and the intermediate frame, and, with this process, atwo-dimensional correlation value profile for each pixel of interest isstored in a correlation value profile memory 169. A sub-pixel processor166 applies the sub-pixel process for each pixel of interest, and anaddress with fractional value for each pixel of interest thus acquiredis stored in a memory 168.

In a similar manner, a matching processor 170 applies the matchingprocess between the subsequent frame and the intermediate frame for eachpixel of interest, and a two-dimensional correlation value profile foreach pixel of interest thus acquired is stored in a memory 172. Asub-pixel processor 179 applies the sub-pixel process for each pixel ofinterest, and an address with fractional value for each pixel ofinterest thus generated is stored in a memory 176. An interpolationprocessor 178 applies the line interpolation process on the intermediateframe using the mapping result of the previous frame and the mappingresult of the subsequent frame. With this process, a frame in which thedensity is increased can be re-constructed.

FIG. 18 shows a first alternative configuration of the ultrasounddiagnosis apparatus. In the first alternative configuration of FIG. 18,a DSC 20A comprises a density increasing unit 18A. In other words, thedensity increasing process and the scan conversion process are appliedat the same time. More specifically, the pattern matching process andthe sub-pixel process are applied for each pixel of the previous frame,and the scan conversion process is applied based on the result of theprocess without independently applying the line interpolation process onthe result of the process. With such a configuration, the lineinterpolation process may be omitted. However, in the scan conversionprocess, a complicated address calculation would be required. In thisfirst alternative configuration also, similar to the basic structuredescribed above, the scan conversion process is executed after thedensity increasing process.

FIG. 19 shows a second alternative configuration of the ultrasounddiagnosis apparatus. In FIG. 19, a density increasing unit 18B isprovided downstream of a DSC 20B. Specifically, the density increasingunit 18B applies a process for increasing the density on a displayframe, and not on the received frame. In other words, the patternmatching process and the sub-pixel process as described above areapplied between display frames, and the line interpolation process isapplied based on the result of these processes. Then, in the densityincreasing unit 18B or in the display processor 22, a thinning processfor conforming with the pixel density of the display screen is appliedon the high-density display frame as necessary. The structure of FIG. 19is preferably employed in cases such as when recording of a highresolution frame is desired.

(2) Density Increasing Using Pattern Matching Process in Frame

FIG. 20 is a block diagram showing another basic structure of anultrasound diagnosis apparatus. The same reference numerals are assignedto common elements as in FIG. 1, and descriptions of these elements willnot be repeated.

In the example configuration of FIG. 20, a density increasing unit 180of an in-frame processing type is provided downstream of the signalprocessor 16. That is, while in the example structure of FIG. 1, thedensity increasing unit of an inter-frame processing type is provided,in the example structure of FIG. 20, there is provided a unit whichapplies the density increasing not between frames but within a frame. Anoperation of this structure will be described with reference to FIGS. 21and 22.

FIG. 21 shows abeam data array 182 in the real space. The beam dataarray 182 comprises a plurality of sets of beam data 184, with each setof beam data 184 having a plurality of data points; that is, a pluralityof pixles 186. Reference numeral 188 represents a tissue present in theliving body. As shown in FIG. 21, in a deep region in the beam dataarray 182, the beam spacing is widened, and the density of the realpixel is reduced.

FIG. 22 shows the in-frame density increasing process as a conceptualdiagram. Reference numeral 202 represents a beam data array; that is, abeam line array. More specifically, a plurality of sets of beam data 189are aligned in the θ direction. The white circles and black circlesrepresent pixels, and, in particular, the black circles represent pixels212 in the tissue. Reference numeral 210 represents a group of pixels212 in the tissue. In the present embodiment, two reference pixel arraysare defined previously and subsequently from the pixel array to beprocessed. More specifically, a first pixel array 209, a second pixelarray 206, and a third pixel array 208 are defined. Here, the secondpixel array 206 is the target pixel array (array of pixels of interest),the first pixel array 204 is the previous pixel array (first referencepixel array), and the third pixel array 208 is the subsequent pixelarray (second reference pixel array). The pixel array of each depth isselected, in order, as the target pixel array. In a pattern matchingprocess 214, a one-dimensional pattern matching process is appliedbetween the first pixel array 204 and the second pixel array 206 for apixel of interest in the first pixel array 204, so that a mappingposition (copy position) of the pixel of interest of the pixel ofinterest on the second pixel array 206 is determined. Similarly, in apattern matching process 216, a one-dimensional pattern matching processis applied between the third pixel array 208 and the second pixel array206 for a pixel of interest in the third pixel array 208, so that amapping position (copy position) of the pixel of interest on the thirdpixel array 208 is determined. Then, an interpolation process 218 isapplied based on a plurality of original, real pixels of the secondpixel array 206 and a plurality of copy pixels (real pixels on otherlines) which are imaginarily or actually mapped on the second pixelarray, so that a high-density pixel array 220 is constructed. Thehigh-density pixel array 220 comprises a plurality of original realpixels 222 of the second pixel array 206, and a plurality ofinterpolation pixels 224 and 226 which are added later to the secondpixel array 206. The interpolation pixel 224 is a pixel in the tissueand the interpolation pixel 226 is a pixel outside of the tissue. Theplurality of interpolation pixels 224 and 226 are set between twoadjacent real pixels 222, and the arrangement of the pixels in the beamscan direction is at equal spacing. When such a process is applied foreach pixel array of each depth, the density of the frame can beincreased using the pixels of the frame itself; that is, are-constructed frame 227 in which the density is increased can beconstructed. Then, as shown by reference numeral 228, the scanconversion process is applied to the re-constructed frame 227, and thedisplay frame is thus generated.

In FIG. 22, each of the pixel arrays 204, 206, and 208 has a thicknessof one pixel in the depth direction. Alternatively, the pixel array mayhave a thickness corresponding to a plurality of pixels. However, in thepattern matching processes 214 and 216, a one-dimensional patternmatching process in the beam scan direction is desirably applied. Thein-frame density increasing process will now be described in more detailwith reference to FIG. 23 and subsequent drawings.

FIG. 23 shows a flowchart of a specific process of the pattern matchingprocesses 214 and 216 shown in FIG. 22. In S30, a pixel of interest isset on a previous line, and, in S32, a one-dimensional template is seton the previous line. In S34, a one-dimensional search area is set onthe current line, and, in S36, a one-dimensional reference area is setin the one-dimensional search area. These processes will be describedwith reference to FIG. 24. In FIG. 24, a plurality of pixel arrays 204,206, and 208 extending in a direction perpendicular to (intersecting)the beam are defined in the beam data array 202, and each pixel arraycomprises a plurality of pixels existing at the same depth. In otherwords, the individual pixel arrays 204, 206, and 208 include a pluralityof pixels aligned in the beamscan direction. In FIG. 24, particularly,the pattern matching process between the first pixel array 204 and thesecond pixel array 206 is shown. The first pixel array 204 correspondsto the previous line, and each pixel in the pixel array is determined asa pixel of interest 230. A template 232 is set centered at the pixel ofinterest 230 and with a width in the beam scan direction. The template232 is a one-dimensional (1D) template. On the other hand, in the secondpixel array 206, a search area 234 is set centered at a point 233corresponding to the pixel of interest 230. A reference area 236 is setin the search area 234. The reference area 236 is a one-dimensionalpixel array having a size similar to that of the template 232. Theone-dimensional pattern matching process is repeatedly applied betweenthe template 232 and the reference area 236 while the position of thereference area 236 is sequentially shifted.

In FIG. 23, in S40, it is judged whether or not the pattern matchingprocess has been applied in all positions of all reference areas in thesearch area, and, if the pattern matching process is not completed forall reference area positions, the processes from S36 are repeatedlyapplied. On the other hand, when it is judged in S40 that the patternmatching process is completed for all reference area positions, in S42,the sub-pixel process is applied. That is, a mapping address withfractional value is calculated for each pixel of interest based on aone-dimensional correlation value profile. This process will bedescribed with reference to FIG. 25. A pixel 238 in the first pixelarray 204 corresponds to a correspondent position 240 on the secondpixel array 206. In other words, the pixel 238 is imaginarily mapped oractually mapped to the correspondent position 240. The correspondencerelationship is shown with reference numeral 242. Similarly, for a pixel246 in the third pixel array 208, a correspondent position 248 on thepixel array 206 is determined. The correspondence relationship is shownwith reference numeral 250. By such a mapping from previous andsubsequent pixel arrays in this manner, the density of the second pixelarray 206 is increased. In other words, the second pixel array in whichthe density is increased includes a plurality of original real pixels244 and a plurality of added pixels (real pixels on other lines) whichare mapped.

In FIG. 23, in S44, it is judged whether or not the above-describedprocess is completed for all pixels on the previous line, and, if theprocess is not completed, the processes from S30 are repeatedlyexecuted. In FIG. 23, the process between the previous line and thecurrent line is shown. However, as can be understood from the abovedescription, a similar process is applied between the subsequent lineand the current line.

FIG. 26 shows a relationship between a beam line 252 and aninterpolation line 256. The beam line (beam data) 252 has a plurality ofpixels 254. Meanwhile, the interpolation line 256 has a plurality ofinterpolation points (interpolation pixels) 258. In the pixel array 206which is currently of interest, as described above, a plurality ofmapped pixels exist in addition to the plurality of real pixels. Asshown in FIG. 27, as a result of the application of the interpolationprocess, an interpolation pixel 262 is generated on the pixel array ofinterest and on each interpolation line. With this process, a pixelarray in which the density is increased can be formed. When theabove-described interpolation process is applied to each pixel array ofeach depth, a data array 202A having a high density as an overall framecan be acquired. Thus, the scan conversion process may be executed basedon the data array 202A, so that a display frame of high density and highquality can be formed.

FIG. 28 shows an example structure of a density increasing unit 180 ofan in-frame processing type shown in FIG. 20. A frame (frame data)before the process is stored in a frame memory 266, and a frame (framedata) after the process is stored in a, frame memory 292. A first linememory 268, a second line memory 270, and a third line memory 272 areconnected in series. A pixel array of the previous line is stored in thefirst line memory 268, a pixel array of the current line is stored inthe second line memory 270, and a pixel array of the subsequent line isstored in the third line memory 272. The one-dimensional matchingprocess and the sub-pixel process are applied between adjacent lines.More specifically, in each of 1D matching processors 274 and 282, amatching process for each pixel of interest is applied between twolines, and a one-dimensional correlation value profile for each pixelacquired as a result of this process is stored in each of respectivememories 276 and 284. Sub-pixel processors 278 and 286 apply thesub-pixel process for each pixel of interest based on theone-dimensional correlation value profile, to determine an address withfractional value for each pixel of interest, and the address withfractional value is stored in memories 280 and 288.

An interpolation processor 290 applies an interpolation process based onthe plurality of real pixels of the target pixel array; that is, thecurrent line, and the plurality of mapping pixels mapped from theprevious and subsequent lines, to re-construct a pixel array in whichthe density is increased, as a result of the interpolation process. There-constructed pixel array is stored in the frame memory 292. When there-constructing process as described above is applied to each pixelarray of each depth, a frame in which the density is increased is formedon the frame memory 292.

FIG. 29 shows an effect of the interpolation process as described above.Specifically, FIG. 29 shows an outline emphasizing effect. Referencenumeral 294 represents a beam line, reference numeral 296 represents aninterpolation line, and reference numeral 298 represents a horizontalline; that is, a line for each depth. Reference numeral 300 representsan outline at a first time phase, reference numeral 302 represents anoutline at a second time phase, and reference numeral 304 represents anoutline at a third time phase. In other words, with the movement of thetissue, the outline is gradually moved in a direction toward the bottomright. White circles represent real pixels and black circles representinterpolation pixels. An arrow shown by reference numeral 310 representsmapping (copying) of the pixel. According to the process shown in thepresent embodiment, as shown on the outline 302, the number of pixels inthe outline can be increased, and, thus, there can be obtained anadvantage that the density of the outline is increased and the outlinecan be displayed in an emphasized manner.

(3) Combined Method and Other Methods

FIG. 30 shows an example combination of the in-frame process and theinter-frame process. In FIG. 30, first in-frame processing type densityincreasing units 312 and 314 are provided in parallel to each other, andthe in-frame process is applied to two frames. Then, in an inter-frameprocessing type density increasing unit 316, the inter-frame process isapplied based on the two frames in which the density is increased. As aresult, a frame in which the density is significantly increased isconstructed, and is output to a DSC 318.

In another example combination shown in FIG. 31, a DSC 322 is provideddownstream of an inter-frame processing type density increasing unit320, and an in-frame processing type density increasing unit 324 isprovided downstream of the DSC 322. In this manner, various combinationsof the in-frame process and the inter-frame process can be considered.Alternatively, the processing content of the density increasing processmay be switched according to an operation mode or a measurementcondition.

In the above-described embodiment, the inter-frame process is based onthe idea that the movement of the tissue is very small between frameswhich are close to each other in time, and that, therefore, the densityof the subsequent frame can be increased by mapping the pixel of theprevious frame to the subsequent frame. On the other hand, the in-frameprocess assumes that a certain similarity relationship exists between apixel array of a certain depth and a pixel array in front of or in backof the pixel array because of the continuity of the tissue in the depthdirection, and the image quality is improved by increasing the densityof the pixel value. Alternatively, the above-described processes may beapplied to volume data. In addition, in the above-described in-frameprocess, the process for the pixel of interest is applied to all pixelsin the pixel array direction, but alternatively, the process for thepixel of interest may be applied only to the pixels belonging to, forexample, a certain portion of a center portion.

What is claimed is:
 1. An ultrasonic image processing apparatuscomprising: a controller configured to include an in-frame processor anda re-constructing unit; the in-frame processor which applies a processbetween a first pixel array and a second pixel array in a frame acquiredby transmitting and receiving ultrasound, and which calculates amovement destination on the second pixel array for each pixel ofinterest in the first pixel array; and the re-constructing unit whichre-constructs the second pixel array into a high-density pixel arrayusing the movement destination calculated for each of the pixel ofinterest, wherein the in-frame processor calculates the movementdestination of the pixel of interest by applying a pattern matchingprocess between the first pixel array and the second pixel array,wherein in the pattern matching process, the in-frame processor; sets atemplate centered at the pixel of interest in the first pixel array;sequentially sets, at different positions in the second pixel array,reference areas each having a size equal to that of the template;generates a correlation value profile by calculating a correlation valuebetween the template and the reference area set at each of thepositions; and calculates a correspondent address on the second pixelarray as the movement destination in accordance with the correlationvalue profile.
 2. The ultrasonic image processing apparatus according toclaim 1, wherein each of the first pixel array and the second pixelarray includes a plurality of pixels arranged in a beam scan direction;a depth of the first pixel array and a depth of the second pixel arraydiffer from each other; and the high-density pixel array includes alarger number of pixels than a number of formations of received beams inthe beam scan direction.
 3. The ultrasonic image processing apparatusaccording to claim 1, wherein the in-frame processor comprises: acorrelation value profile generating unit which generates a correlationvalue profile as a result of the pattern matching process for each pixelof interest in the first pixel array; and a correspondent addresscalculating unit which calculates a correspondent address on the secondpixel array as the movement destination based on the correlation valueprofile for each pixel of interest in the first pixel array.
 4. Theultrasonic image processing apparatus according to claim 3, wherein thecorrespondent address is a correspondent address with a fractionalvalue, including an integer part corresponding to an integer multiple ofan original pixel spacing in the second pixel array and a fractionalvalue smaller than the original pixel spacing.
 5. The ultrasonic imageprocessing apparatus according to claim 4, wherein the re-constructingunit re-constructs the high-density pixel array by an interpolationprocess based on an original group of pixels of the second pixel arrayand an additional group of pixels defined by a pixel value and thecorrespondent address with fractional value for each pixel of interest.6. The ultrasonic image processing apparatus according to claim 1,wherein a high-density frame is formed by re-constructing a plurality ofpixel arrays of the frame into a plurality of high-density pixel arrays,and the high-density frame includes a plurality of sets of original beamdata and a plurality of sets of interpolation beam data.
 7. Theultrasonic image processing apparatus according to claim 1, wherein thepixel of interest is selected in a partial region in the first pixelarray and the second array, and the high-density pixel array is a pixelarray in a part of which the density is increased.
 8. The ultrasonicimage processing apparatus according to claim 1, wherein the in-frameprocessor calculates, by a process between the second pixel array and athird pixel array in the frame acquired by transmitting and receivingultrasound, a movement destination on the second pixel array for eachpixel of interest in the third pixel array, and the re-constructing unitre-constructs the second pixel array into the high-density pixel arrayusing the movement destination calculated for each pixel of interest inthe first pixel array and the movement destination calculated for eachpixel of interest in the third pixel array.
 9. The ultrasonic imageprocessing apparatus according to claim 7, wherein the frame comprisesan ultrasonic beam array which is spread radially, and the high-densityframe includes a plurality of interpolation lines which are added atleast in a deep portion of the frame.
 10. The ultrasonic imageprocessing apparatus according to claim 1, wherein the frame is a framewhich conforms with a transmission/reception coordinate system, ahigh-density frame is formed by repeatedly applying the re-constructionof the high-density pixel array, and there is provided a conversion unitwhich generates a display frame which conforms with a display coordinatesystem from the high-density frame.
 11. The ultrasonic image processingapparatus according to claim 1, wherein the frame is a frame which isacquired in real time or a frame which is read from a cine memory. 12.The ultrasonic image processing apparatus according to claim 1, furthercomprising: a unit which applies a pre-process to increase density ofthe frame by an inter-frame interpolation process before the frame isinput to the in-frame processor.
 13. The ultrasonic image processingapparatus according to claim 1, further comprising: a unit which appliesa post-process to further increase the density of a high-density framegenerated by repeatedly applying the re-construction of the high-densitypixel array or to further increase the density of a display frameacquired based on the high-density frame.
 14. An ultrasonic imageprocessing apparatus, comprising: a controller that includes an in-frameprocessor which applies a process between a first pixel array and asecond pixel array in a frame which is acquired by transmitting andreceiving ultrasound and which conforms with a transmission/receptioncoordinate system, and which calculates a movement destination on thesecond pixel array for each pixel of interest in the first pixel array,and a conversion unit which applies a process to convert the frame whichconforms with the transmission/reception coordinate system into adisplay frame which conforms with a display coordinate system, and whichrefers to a pixel value for each of the pixel of interest and themovement destination for each of the pixel of interest during theconversion process, wherein the in-frame processor calculates themovement destination of the pixel of interest by applying a patternmatching process between the first pixel array and the second pixelarray, wherein in the pattern matching process, the in-frame processorsets a template centered at the pixel of interest in the first pixelarray; sequentially sets, at different positions in the second pixelarray, reference areas each having a size equal to that of the template;generates a correlation value profile by calculating a correlation valuebetween the template and the reference area set at each of thepositions; and calculates a correspondent address on the second pixelarray as the movement destination in accordance with the correlationvalue profile.
 15. A non-transitory computer-readable storage mediumwith an executable ultrasonic image processing program stored thereonwhich is executed by an information-processing device, comprising;applying a process between a first pixel array and a second pixel arrayin a frame acquired by transmitting and receiving ultrasound, andcalculating a movement destination on the second pixel array for eachpixel of interest in the first pixel array, and re-constructing thesecond pixel array into a high-density pixel array using the movementdestination calculated for each of the pixel of interest, wherein thein-frame processor calculates the movement destination of the pixel ofinterest by applying a pattern matching process between the first pixelarray and the second pixel array, wherein in the pattern matchingprocess, the in-frame processor sets a template centered at the pixel ofinterest in the first pixel array; sequentially sets, at differentpositions in the second pixel array, reference areas each having a sizeequal to that of the template; generates a correlation value profile bycalculating a correlation value between the template and the referencearea set at each of the positions; and calculates a correspondentaddress on the second pixel array as the movement destination inaccordance with the correlation value profile.